/*
 * Copyright (c) 2001, University of Washington, Department of
 * Computer Science and Engineering.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following
 * disclaimer in the documentation and/or other materials provided
 * with the distribution.
 *
 * 3. Neither name of the University of Washington, Department of
 * Computer Science and Engineering nor the names of its contributors
 * may be used to endorse or promote products derived from this
 * software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package one.world.core;

/**
 * The superclass of all symbolic event handlers. Unlike regular event
 * handlers, symbolic event handlers do not directly provide any
 * functionality. Rather, they carry some symbolic information that
 * represents an actual event handler. As a result, symbolic event
 * handlers are not wrapped when crossing concurrency domain or
 * protection domain boundaries.
 *
 * @see      Wrapper
 *
 * @version  $Revision: 1.3 $
 * @author   Robert Grimm
 */
public abstract class SymbolicHandler
  implements EventHandler, java.io.Serializable {

  /** The serial version ID for this class. */
  static final long serialVersionUID = -3846386834653411023L;

  /** Create a new symbolic event handler. */
  public SymbolicHandler() {
    // Nothing to do.
  }

  /**
   * Handle an event. This handler sends an exceptional event that
   * wraps an unsupported operation exception to the source of the
   * specified event, unless the specified event is an exceptional
   * event, in which case the event is simply logged.
   *
   * @throws  UnsupportedOperationException
   *             Signals that symbolic event handlers do not actually
   *             handle events.
   */
  public final void handle(Event e) {
    SystemLog.LOG.logError(this, "Unexpected event for symbolic handler (" + e +
                           ")");

    if ((null != e.source) && (! (e instanceof ExceptionalEvent))) {
      e.source.handle(new
        ExceptionalEvent(this, e.closure, new
          UnsupportedOperationException("Symbolic handler invoked (" + this +
                                        ")")));
    }
  }

}
